Systems and methods for multiple input instrumentation buses

ABSTRACT

Systems and methods for multiple input instrumentation buses are disclosed. In one embodiment, a bus assembly includes a control module adapted to be coupled to a network, and a plurality of nodes operatively coupled in a linear topology. A plurality of interface modules are coupled to the nodes. At least one node is adapted to receive a primary response signal from the correspondingly coupled interface module, and a secondary response signal from at least one other node, and to determine which of the primary and secondary response signals arrived first, and to output a corresponding one of the primary and secondary response signals that arrived first.

FIELD OF THE INVENTION

This invention relates to data buses, and more specifically, to improvedsystems and methods for multiple input instrumentation buses for usewith, for example, distributed multidrop transducer systems andnetworks.

BACKGROUND OF THE INVENTION

Some types of instrumentation systems involve the interfacing of aplurality of inputs from multiple transducers and other input sources.To address these circumstances, the Institute of Electrical andElectronics Engineers (IEEE) Standards Association has developed astandard for interfacing multiple, physically separated transducers thatallows for the time synchronization of data, known as IEEE 1451.3“Standard for a Smart Transducer Interface for Sensors and Actuators,Digital Communication and Transducer Electronic Data Sheet (TEDS)Formats for Distributed Multidrop Systems.” In brief, the standardattempts to provide a minimum implementation for theself-identification, multidrop, hot swapping and configuration oftransducers in such instrumentation systems and networks.

For example, FIG. 1 is a multidrop instrumentation system 100 ascontemplated by the IEEE 1451.3 standard. The system 100 includes afirst transmission line 102 coupled between a Transducer Bus Controller(TBC) 104 of a Network Capable Application Processor (NCAP) 108 and aplurality of Transducer Bus Interface Modules (TBIM) 106. The firsttransmission line 102 is used to supply power to the TBIMs 106 and tocarry communication signals between the TBIMs 106 and the bus controller104. A second transmission line 103 serves as a network communicationschannel and is used to establish the basic network communications thatallows the bus controller 104 to determine the capabilities andconfiguration of each TBIM 106. This portion between the TBIMs and TBCis considered the physical layer of the system. In turn, the NCAP 108 iscoupled to a network 110, and contains the bus controller 104 and aninterface to the network 110 that may support many other buses. EachTBIM 106 may contain one or more different transducers or other signalgenerators.

Although desirable results have been achieved using such systems, theIEEE 1451.3 standard may not be reliable or suitable for some types ofdistributed multidrop transducer systems and networks.

SUMMARY OF THE INVENTION

The present invention is directed to systems and methods for multipleinput instrumentation buses. Embodiments of the present invention mayadvantageously reduce propagation delays, may consume less power, maycost less, and may operate more robustly in a wider variety ofenvironments in comparison with prior art systems.

In one embodiment, a bus assembly includes a control module adapted tobe coupled to a network, and a plurality of nodes operatively coupled ina linear topology. A first one of the nodes is coupled to the controlmodule. The bus assembly further includes a plurality of interfacemodules, each interface module being coupled to a corresponding one ofthe nodes. At least one node is adapted to receive a primary responsesignal from the correspondingly coupled interface module and a secondaryresponse signal from at least one other node, and to determine which ofthe primary and secondary response signals arrived first, and to outputa corresponding one of the primary and secondary response signals thatarrived first. In another embodiment, the interface modules may beadapted to communicate using a set of point-to-point linear Ethernetcommunications. In a further embodiment, the interface modules areadapted to communicate using a communication unit that includes at leastone of an isochronous portion and an asynchronous portion.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are described in detail below withreference to the following drawings.

FIG. 1 is a multidrop instrumentation system in accordance with theprior art;

FIG. 2 is a transducer bus for a multidrop instrumentation system inaccordance with an embodiment of the present invention;

FIG. 3 shows a transmission of a representative packet that occupies asingle time slot that may be applicable for an embodiment of theinvention;

FIG. 4 is a schematic representation of a TBIM node in accordance withan embodiment of the invention;

FIG. 5 shows an epoch unit of time that may be applicable for anembodiment of the invention;

FIG. 6 shows a graph comparing an estimated propagation delay (T_(pd))through a transducer bus with prior art systems in accordance withanother embodiment of the invention;

FIG. 7 is an isometric view of a multiple input instrumentation systemin accordance with an embodiment of the invention;

FIG. 8 is an enlarged view of a pair of units of the system of FIG. 7;and

FIG. 9 is an enlarged bottom view of a TBIM of the system of FIG. 7.

DETAILED DESCRIPTION

The present invention relates to systems and methods for multiple inputinstrumentation buses. Many specific details of certain embodiments ofthe invention are set forth in the following description and in FIGS.2-9 to provide a thorough understanding of such embodiments. The presentinvention may have additional embodiments, or may be practiced withoutone or more of the details described for any particular describedembodiment.

FIG. 2 is a transducer bus 200 for a multidrop instrumentation system inaccordance with an embodiment of the present invention. In thisembodiment, the transducer bus 200 includes a Transducer Bus Controller(TBC) 204 and a plurality of Transducer Bus Interface Modules (TBIMs)206. Each TBIM node (or eNode) 208 is coupled to another correspondingTBIM node (or eNode) 208 by a plurality of pairs of conductors 202 a(e.g. three or four pairs). Each (TBIM) 206 is coupled to the TBIM node208 by the Physical Independent Interface (or PII) 202 b. Similarly,adjacent TBIM nodes 208 are coupled by pairs of conductors 202 a, andthe TBC node (or eNode) 209 is coupled to the TBIM node 208 by the pairsof conductors 202 a. The TBC 204 is coupled to a TBC node 209 by the PII202 b. The pairs of conductors 202 a carry both the power and thesignals to implement the transducer bus 200. The conductors in the PII202 b carry the signals necessary to implement the Physical IndependentInterface between the TBIM node 208 and the TBIM 206 or the TBC node 209and the TBC 204.

As shown in FIG. 2, each TBIM 206 is coupled via the TBIM nodes 208 in alinear or “daisy chain” topology to the other components of thetransducer bus 200. This may be accomplished by adapting each TBIM node208 to function in a terminate and repeat mode, which means that allpackets from the TBC 204 received by every TBIM node 208 on the bus 200would be clocked in, buffered, and clocked out the other side.Similarly, all packets returning to the TBC 204 would be routed througha switch within each TBIM node 208, with a first event detect circuitcontrolling the switch, as described more fully below with respect toFIG. 4.

The following describes how particular embodiments of the invention maybe used within the context of IEEE 1451.3 and IEEE 802.3. Morespecifically, in one embodiment, the communication of each TBIM 206 isimplemented using a combination of point-to-point 100BASE-T LinearEthernet communications based on IEEE Std. 802.3-2002 standard, andtransducer bus specific signals. The transducer bus 200 combines power,a composite signal, and Ethernet communication signals on the pairs ofconductors 202 a, consisting of a transmit pair, a receive pair, acomposite pair and a power pair. In one embodiment, the composite signalis a pulse width modulated signal combining a synchronization signal(e.g. 2 MHz) and an epoch signal. The synchronization signal may assurethat all TBIMs 206 on the bus 200 have access to a clock running at thesame frequency.

More specifically, in one aspect, the Ethernet data link layerspecifications may be those provided in Paragraph 22 of IEEE Std.802.3-2002, incorporated herein by reference, which includes error,collision, carrier sense and management signals. In another aspect,however, a collision avoidance strategy is superimposed on thetransducer bus 200 wherein the bus executes in an isochronous modefollowed by an asynchronous mode within a periodic interval called anEpoch. The TBIMs 206 detect and keep track of the communication modesbased on information decoded from the composite signal. In oneparticular embodiment, the data rate is 100 Mb/s and uses a 4B/5B blockcoding scheme, and the mode is full duplex. A dedicated eight wire bussegment 202 a is connected between the TBIM nodes 208, or between theTBC node 209 and the TBIM nodes 208. This may be referred to as apoint-to-point Linear Ethernet bus segment.

Isochronous communication may be based on a Time Division MultipleAccess (TDMA) allocation of bandwidth, such that each TBIM 206 on thetransducer bus 200 may have a dedicated portion of an interval duringwhich it may transmit messages, and is then prohibited from transmittingduring the remainder of that interval. The transducer bus 200 mayperiodically have an isochronous interval during which these rulesprevail. The TBC 204 subdivides the isochronous interval into a fixednumber of time slots and allocates unique slots to each activetransducer channel. The number of adjacent time slots assigned to atransducer channel is preferably large enough to transmit a completemessage.

FIG. 3 shows a transmission of a representative packet that occupies asingle time slot 300 that is applicable for an embodiment of theinvention. In this embodiment, the time slot 300 is a time interval thatis divided into four segments. First, a start time uncertainty segment302 is the maximum time required by the TBC 204 or the TBIM 206 to placethe frame on the bus 200 after the start of the time slot 300. The starttime uncertainty segment 302 is a function of the design and may bezero. Next, a data packet segment 304 is the time available to transmitthe packet of data. An Inter Frame Gap (IFG) segment 306 is a mandatorydead time on the bus 200 between the end of one transmission and thestart of the next transmission. Finally, a fourth segment 308 is anunused portion of the time slot 300. As further shown in FIG. 3, in oneparticular embodiment, the time slot 300 has a predefined time of 200microseconds (μs), and the Ethernet defines the data portion of acommunication frame as a maximum of 1500 bytes. With 18 bytes ofoverhead, a frame requires 121.44 μs with a minimum silence time of 960nanoseconds (ns). Because of the minimum silence time requirement, acommunication frame may occupy the first 122.4 μs of the allocated slot.

The time slots may be numbered beginning with slot zero, which is usedby the TBC 204 to transmit the beginning of the epoch message. The lasttime slot in the isochronous interval may be used to transmit the startasynchronous interval message. In a streaming mode, a transducer channelwill acquire a data set and initiate transmission during its assignedtime slot in the isochronous interval. The length of a transmissioninterval (in time slots) is preferably long enough to transmit theentire data set. A maximum-sized data set is defined as the largest dataset that will fit within a message transmitted using a Streaming DataProtocol. A message of this size will be fragmented into packets by theLogical Link Control (LLC) layer, as described below. Despite a generousunused portion of the time slot 300, an algorithm used at the NCAP toallocate time slots may be based on one slot per packet. If a transducerchannel is sampling data at a rate lower than the epoch rate so that itdoes not have data to transmit during that epoch, the time slot may gounused.

In further embodiments, asynchronous communications may be used. In someembodiments, asynchronous communication may be initiated at will. Morespecifically, the transducer bus 200 may periodically have anasynchronous interval during which this is possible. To support bothasynchronous and isochronous communication, the transducer bus 200 maycyclically alternate between these communication modes. Asynchronouscommunication may therefore be initiated during the asynchronousinterval.

During the asynchronous interval, however, two TBIMs 206 can initiate atransmission simultaneously. In cases where an unconstrained topology isemployed, this simultaneous transmission would result in a collision.Therefore, embodiments of the present invention may include anarbitration at each node 208, 209 that allows only one response tosucceed. The other response may be discarded without the sender'sknowledge. This strategy is called “survival of the first”, and it helpsto ensure that the Ethernet MAC/PHY perceives an available media anddoes not engage collision detection, back off, and retransmission. The“survival of the first” transmission strategy also accommodatesprecision timing for the duration of the asynchronous and isochronousintervals.

FIG. 4 is a schematic representation 400 of a TBIM node 208 adapted toimplement the “survival of the first” strategy in accordance with anembodiment of the invention. In this embodiment, a first receivingmodule 402 is coupled to a first lead 404 of an incoming pair ofconductors 202, and is adapted to receive a command from the TBC 204(FIG. 2). The command is then transmitted via a second lead 406 to theTBIM 206 corresponding to the TBIM node 208 and to a First-In-First-Out(FIFO) buffer 408 of a first transmit component 410. The command istransmitted by the first transmit component 412 along a third lead 412to the next daisy-chained TBIM node 208 in the transducer bus 200. Asecondary response may be received along a fourth lead 414 into a FIFObuffer 416 of a second receive component 418. The secondary response istransmitted along a fifth lead 420 to a switch component 422, and alonga sixth lead 424 to a first event detector 426. Also, a TBIM response istransmitted from the TBIM 206 along a seventh lead 428 to the switchcomponent 422, and along an eighth lead 430 to the first event detector426. The first event detector 426 is adapted to receive the secondaryresponse and the TBIM response, and to determine which response arrivedfirst. Based on this determination, the first event detector 426controls the switch component 422 to cause the first-arriving responseto be sent to the second transmit component 432 along a ninth lead 434,and subsequently out of the TBIM node 208 via a tenth lead 436.

Since each TBIM node 208 operates in the terminate-and-repeat mode, eachnode-to-node segment of the transducer bus 200 acts as a dedicatedpoint-to-point connection. Therefore, any number of TBIM nodes 208 (andTBIMs 206) may be added to the bus 200 as long as the conductors 202 areadapted to provide sufficient power.

The “survival of the first” strategy may be advantageous for atransducer bus 200 on which asynchronous traffic is characterized asCommand-Response. For most commands, there is only one or no responder.One exception may be a discovery command wherein discarding thecompeting responses simplifies the TBC logic. More specifically, the TBC204 may issue a discovery request and gets a single response from one ofthe TBIMs 206 that prevailed over all of its competitors in the“survival of the first” environment. The TBC 204 assigns an alias tothat TBIM 206 and issues another discovery request. This process maycontinue until the discovery request fails to solicit a response fromany TBIM 206. In one particular embodiment, however, if solicitedre-transmissions are not desired, then the asynchronous time slots maybe omitted, as described more fully below.

In the “survival of the first” topology, there preferably will be nocollisions with retransmission as there may be in an HPNA-based (HomePhoneline Network Adapter) topology. Therefore, in another aspect of theinvention, some type of discipline may be imposed on the asynchronousperiod 504 similar to the isochronous period 502. Isochronous time slots(ITS) are assigned by the TBC 206. By implementing asynchronous timeslots (ATS), which may be either fixed or assigned by the TBC 206, thedesired discipline may be imposed on the asynchronous period 504. Forexample, in one particular embodiment, a first ATS may be fixed to mean“try until acknowledged”. In this case, all TBIM's 208 with infrequentor non-time critical data would continually transmit their data onceduring each epoch, until the TBC 206 acknowledges receipt of the packet.This alternative may suitably be used to handle any discarded packetsresulting from the “survival of the first” operation.

In another aspect, a second ATS could be fixed to mean “send UUIDinformation”. With the second ATS, all un-configured TBIM's connected tothe bus could transmit their UUID (Universal Unique Identifier)information once per epoch (described below with reference to FIG. 5),until the TBC 206 responds with the configuration information.

In further aspects, 7 ATS numbers could be assigned to “retransmit lastdata packet”. With this assignment, if the NCAP determines that a packetfrom an individual TBIM is corrupted and needs to be sent again, theretransmission request would include the ATS for the transmission. Thiscould be extended, for example, if more than 7 packets need to betransmitted again.

In embodiments of the present invention, time may be organized intouniformly timed blocks called epochs. FIG. 5 depicts an epoch 500. Inthis embodiment, each epoch 500 is subdivided into an isochronousinterval 502 and an asynchronous interval 504. The time allocated to theisochronous interval 502 varies and is dependent on the number of TBIMs206 and the transmission time each TBIM 206 requires. The current modeof operation of the bus 200 (isochronous or asynchronous) may bedetermined by decoding the composite signal to obtain an epoch marker406 that demarcates the beginning and end of the intervals. The TBC 204may assign the length of both the isochronous and asynchronous intervals502, 504 to the bus 200 with a broadcast of a “Define epoch” message.The assignment may be in the form of time slot counts. In turn, theTBIMs 206 may count time slots to detect when their assigned isochronousslot 502 begins, so that they may send their message, and when theasynchronous interval 504 begins. This information may be used to ensurethat as the asynchronous interval 504 approaches the end, an impendingtransmission does not overflow into the next isochronous interval 502.

In particular embodiments, for example, the time length of an epoch is amultiple of a slot time, and the epoch length (the sum of theisochronous interval 502 and the asynchronous interval 504) does notexceed 250 milliseconds (ms). Similarly, in some embodiments, the timelength of the isochronous interval 502 may be a multiple of the slottime, and may have a minimum length of 400 μs (e.g. 2 slots), and amaximum length of 240 ms. In still further embodiments, the time lengthof the asynchronous interval 504 may be a multiple of the slot time, andmay have a minimum length of 10 ms.

Embodiments of the present invention may provide significant advantagesover the prior art. For example, the propagation delay of data passingthrough the transducer bus 200 may be improved in comparison with otherprior art alternatives. More specifically, in one embodiment, it takesapproximately 40 nanoseconds (ns) to get each nibble, i.e. 4 bits, ofdata into a repeater (or Command MII FIFO) within each TBIM node 208 inorder to pass the unchanged data through to the next bus segment, e.g.TBIM 206 or another TBIM node 208. If we assume that it takes anotherapproximately 40 ns to clock each nibble out of the repeater, then addanother approximately 20 ns for delay through the logic, this adds up toapproximately 100 ns. If we multiply this figure by a safety factor offive, we can estimate that the propagation delay through each TBIM node208 is approximately 0.5 μs. This delay does not change with the size ofthe packet. However, each TBIM node added to the transducer bus 202 amay add this propagation delay to the total transducer bus propagationdelay. FIG. 6 shows a graph 700 comparing an estimated propagation delay(T_(pd)) 702 through a transducer bus having 32 TBIM nodes 208 withcorresponding propagation delays 704 through variouscommercially-available HPNA-based buses in accordance with the priorart. Based on the data shown in FIG. 6, embodiments of the presentinvention may advantageously reduce the propagation delay T_(pd) of datapassing through buses in comparison with other prior art alternatives.

Furthermore, embodiments of the present invention may advantageouslyemploy one or more of the upper layers of the IEEE 1451.3 protocol, asused for an HPNA-based solution. Since embodiments of the presentinvention may employ carrier class Ethernet components, these componentsmay be suited to operate in harsh environments for longer periods,including environments that include low-grade cabling, highelectromagnetic interference, and extreme temperatures. Embodiments ofthe present invention may require less power in comparison withalternate HPNA implementations, and may have greater availability andlower cost in comparison with alternate prior art systems.

It will be appreciated that embodiments of the present invention may beimplemented in a variety of systems and networks that include multipleinput instrumentation buses for use with, for example, multipledistributed transducers. For example, FIG. 7 is an isometric view of amultiple input instrumentation system 800 in accordance with anembodiment of the invention. FIG. 8 is an enlarged view of a pair ofTBIMs 802 of the system 800 of FIG. 7. FIG. 9 is an enlarged topisometric view of a TBIM 802 of the system 800 of FIG. 7.

In the embodiment shown in FIGS. 7-9, the multiple input instrumentationsystem 800 includes a pair of units 801, each having a TBIM node 808placed on top of a TBIM 806. A Network Capable Application Processor(NCAP) 810 is coupled to the TBIMs 806 by cables 811, each cable 811having, in one particular embodiment, four pairs of conductors.Transmission lines 805 couple the units 801 to each other and to othercomponents (e.g. sensors, transducers, memory device, processor,Ethernet, etc.) of the system 800. In some embodiments, the transmissionlines 805 may be used to program the TBIMs 806.

As best shown in FIG. 9, each TBIM 806 has a connector 807 adapted forcoupling the TBIM 806 with its corresponding TBIM node 808 (FIGS. 7 and8). The TBIM 806 includes a printed wiring assembly (PWA) 814. In oneembodiment, the PWA 814 includes an Ethernet daughter card 816 thatimplements the TBIM node 808, and a TBIM PWA 818. FIG. 9 shows the nearside of the TBIM PWA 818 with the Ethernet daughter card 816 removed.The Ethernet daughter card 816 and the TBIM PWA 818 may be connectedtogether using, for example, one or more 100 pin mating connectors. Thisinterface may be the PII. A similar Ethernet daughter card may becontained inside the NCAP 810 and may serve as a TBC node, and may alsointerface via the PII to a TBC main board.

While preferred and alternate embodiments of the invention have beenillustrated and described, as noted above, many changes can be madewithout departing from the spirit and scope of the invention.Accordingly, the scope of the invention is not limited by the disclosureof these preferred and alternate embodiments. Instead, the inventionshould be determined entirely by reference to the claims that follow.

1. A bus assembly, comprising: a control module adapted to be coupled toa network; a plurality of nodes operatively coupled in a lineartopology, a first one of the nodes being further coupled to the controlmodule; and a plurality of interface modules, each interface modulebeing coupled to a corresponding one of the nodes, wherein at least onenode is adapted to receive a primary response signal from thecorrespondingly coupled interface module and a secondary response signalfrom at least one other node, and to determine which of the primary andsecondary response signals arrived first, and to output a correspondingone of the primary and secondary response signals that arrived first. 2.The bus assembly of claim 1, wherein at least one node is furtheradapted to receive a control signal and to transmit the control signalto at least one other node and to the correspondingly coupled interfacemodule.
 3. The bus assembly of claim 1, wherein the at least one node isfurther adapted to discard the other of the primary and secondaryresponse signals that did not arrive first.
 4. The bus assembly of claim1, wherein the control module includes a transducer bus controller and acontroller node coupled to the transducer bus controller and to thefirst one of the nodes, and wherein the plurality of interface modulesincludes at least one transducer bus interface module.
 5. The busassembly of claim 1, wherein the interface modules are adapted tocommunicate using a set of point-to-point linear Ethernetcommunications.
 6. An instrumentation system, comprising: a plurality ofinput sources; a communication link; and a bus assembly operativelycoupled to the plurality of input sources and to the communication link,the bus assembly including: a control module operatively coupled to thecommunication link; a plurality of nodes operatively coupled in a lineartopology, a first one of the nodes being further coupled to the controlmodule; and a plurality of interface modules, each interface modulebeing coupled to a corresponding one of the nodes, wherein at least onenode is adapted to receive a primary response signal from thecorrespondingly coupled interface module and a secondary response signalfrom at least one other node, and to determine which of the primary andsecondary response signals arrived first, and to output a correspondingone of the primary and secondary response signals that arrived first. 7.The system of claim 6, wherein the at least one node is further adaptedto receive a control signal and to transmit the control signal to atleast one other node and to the correspondingly coupled interfacemodule.
 8. The system of claim 6, wherein the asynchronous portionincludes a discipline scheme to prevent collisions between responses ofsimultaneously responding interface modules.
 9. The system of claim 6,wherein the asynchronous portion includes a discipline scheme having aplurality of asynchronous time slots.
 10. A method of transmittinginformation along a multidrop bus, comprising: providing a plurality ofnodes operatively coupled in a linear topology; providing a plurality ofinterface modules, each interface module being coupled to acorresponding one of the nodes; receiving a primary response signal at afirst one of the nodes from the correspondingly coupled interfacemodule; receiving a secondary response signal at the first one of thenodes from at least one other node; determining which of the primary andsecondary response signals arrived earlier; and outputting theearlier-arriving one of the primary and secondary response signals. 11.The method of claim 10, further comprising receiving a control signaland transmitting the control signal to the at least one other node andto the correspondingly coupled interface module.
 12. The method of claim10, further comprising discarding the other of the primary and secondaryresponse signals that did not arrive first.
 13. The method of claim 10,wherein at least one of the receiving a primary response signal, andreceiving a secondary response signal, and outputting theearlier-arriving one using a communication unit that includes at leastone of an isochronous portion and an asynchronous portion.
 14. Themethod of claim 10, wherein communicating using an isochronous portionincludes communicating using an isochronous portion based on a TimeDivision Multiple Access (TDMA) allocation of bandwidth.
 15. The methodof claim 10, wherein communicating using an asynchronous portionincludes communicating using an asynchronous portion based on adiscipline scheme to prevent collisions between responses ofsimultaneously responding interface modules.
 16. The method of claim 10,wherein communicating using an asynchronous portion includescommunicating using an asynchronous portion based on a discipline schemehaving a plurality of asynchronous time slots.
 17. The method of claim16, wherein communicating using an asynchronous portion based on adiscipline scheme having a plurality of asynchronous time slots includescommunicating using an asynchronous portion wherein a corresponding oneof the asynchronous time slots has a value corresponding to at least oneof a try until acknowledged command, a send UUID command, and aretransmit last data packet command.